Magnetic recording materials, such as video tapes, audio tapes, memory tapes and floppy disks, are constructed fundamentally of a non-magnetic support and a magnetic layer provided thereon. The magnetic layer has as its predominent constituents ferromagnetic particles, a binder and additives (e.g., an antistatic agent, a lubricant, etc.). The ferromagnetic particles are generally made up of acicular or an cubic iron oxide, chromium oxide or certain alloys, and are uniformly oriented in the direction of magnetic recording (for instance, in the longitudinal direction of a magnetic tape in the case of a recording system which utilizes a longitudinal component of magnetization) in the magnetic layer.
In recent years, vertical magnetization recording systems have been proposed (in, e.g., U.S. Pat. No. 4,210,946) for the purpose of recording a large amount of information in a small area of a magnetic material. Ferromagnetic particles employed in such systems differ from conventional ones in having a plate-like shape. More specifically, so-called hexagonal plate-shaped particles, such as barium ferrite, strontium ferrite and the like, are employed as the ferromagnetic particles therein. In such systems, various investigations for increasing the output of plate-shaped ferromagnetic particles in the short wave-length region have been made and reported in, for example, U.S. Pat. No. 4,341,648 and Japanese Patent Application (OPI) Nos. 67904/81 and 134522/81.